This invention relates generally to a video graphics system and, more particularly, to a low cost method and apparatus for combining relatively low resolution text and graphics normally displayed on a home computer video monitor with relatively high resolution graphics normally displayed on a relatively high resolution vector monitor.
Raster scan display devices are typically used to display relatively low resolution text and graphics images. As is well known in the art, the electron beam from a cathode ray tube scans across the entire monitor screen, one line at a time, in response to horizontal and vertical sync signals. The scan pattern is repeated about 60-72 times per second and the resultant image is integrated by the human eye. A typical raster scan image can exhibit aliasing, which depends upon the size of the displayed pixels and is characterized by jagged edges on a sharply sloped line segment, instead of a smooth edge.
Vector displays are typically used to display relatively high resolution images such as are found in a cardiographic ECG waveform, or other biological waveforms. As is well known in the art, the position of the electron beam from the cathode ray tube is controlled by orthogonal plates and can be moved from one point on the display screen to any other point. A repetitive waveform can be constantly written to the screen, under control of an input sync waveform, which can be the input signal itself, or other waveforms such as the power line waveform. Vector waveforms do not exhibit aliasing, because even sharply sloped line segments are constructed of a single sweep of the electron beam, and not successive scanned lines.
Lower resolution text and graphics provided by a home computer are easily combinable with the relatively higher resolution biological waveforms if an expensive high resolution (one million pixels or more) raster scan display is used, although some aliasing can still be present. The two different resolution graphics images are typically not combinable on a single vector display.
Accordingly, a need remains for a convenient method and apparatus for combining lower resolution text and graphics with higher resolution biological waveforms without the use of an expensive high resolution raster scan video monitor.